1. Field of the Invention
This invention relates to a method for extending the pot-life of a curable composition comprising a mixture of at least one active hydrogen-containing material, such as a polyol or a polyamine, and at least one polyisocyanate by incorporating within the mixture a pot-life extending amount of a polyanhydride having an average of at least about two anhydride groups per molecule. This invention also relates to multi-component curable compositions comprising:
(i) at least one polyol or polyamine; PA0 (ii) a polyisocyanate; and PA0 (iii) a polyanhydride. PA0 (i) a material having at least two active hydrogen groups per molecule, such as a polyol or a polyamine, PA0 (ii) a polyisocyanate, and PA0 (iii) a pot-life extending amount of a polyanhydride compound PA0 (i) at least one active hydrogen-containing material, especially a polyol or polyamine; and PA0 (ii) a polyisocyanate; and PA0 (iii) a polyanhydride having an average of at least about two anhydride groups per molecule. PA0 (i) at least one polyol or polyamine, PA0 (ii) a polyisocyanate, and PA0 (iii) a polyanhydride.
The curable compositions of this invention are especially useful as coatings and may typically be utilized as primers, topcoats or as clearcoats and/or basecoats in clearcoat/basecoat compositions. In particular, the combination of at least one polyol or polyamine, a polyisocyanate and a polyanhydride provides fast reacting, durable coatings having extended pot-life and excellent cure. The compositions of this invention could also be utilized as adhesives, elastomers and plastics.
2. Description of the Prior Art
Two-component curable mixtures comprising polyisocyanates and active hydrogen-containing compounds, such as polyols or polyamines, are well-known in the art to provide excellent performance and cure at low temperatures. However, due to the reactivity of the isocyanates and the active hydrogen-containing compounds, it is often difficult to obtain long pot-lifes of the mixture of polyisocyanate and active hydrogen-containing material and yet still enjoy the benefits of rapid cure. This is especially true for low VOC materials, which will incorporate relatively low levels of solvent and will frequently involve low molecular weight, but highly reactive, starting materials.
A number of approaches to extending the pot-life of mixtures of polyisocyanates and active hydrogen-containing compounds, have been taught in the prior art. For example, U.S. Pat. No. 4,426,510 teaches the use of beta-dicarbonyl compounds, alphahydroxy ketones, fused aromatic beta-diketones and beta-hydroxy nitrogen-heterocyclic fused aromatics as pot-life extenders for certain metal catalyzed polyol/polyisocyanate combinations. U.S. Pat. No. 4,235,766 teaches the addition of certain 2-methyl-2-alkanols to extend the pot-life of isocyanate/polyol mixtures. U.S. Pat. No. 4,096,128 teaches the use of certain triazoles to extend the pot-life of isocyanate/diamine mixtures. U.S. Pat. No. 4,019,933 teaches use of reaction products of tri-functional aziridinyl phosphine oxides with carboxylic acids to extend pot-life. U.S. Pat. No. 4,184,031 teaches the use of a composition of matter comprising a metallo organic compound and a carboxylic acid, or a compound convertible thereto, such as a carboxylic anhydride, by reaction with an active hydrogen compound. U.S. Pat. No. 4,877,829 teaches the use of organic and inorganic acids, such as benzoyl chloride, p-toluene sulfonic acid, formic acid, acetic acid, benzoic acid, phosphoric acid, hydrochloric acid and the like. The prior art has not, however, taught the combination of:
to provide low temperature curing, extended pot-life materials having excellent durability, hardness and performance upon cure. In addition to extending the pot-life of the isocyanate based system, the polyanhydrides also provide an additional mechanism for curing active hydrogen materials such as polyols and polyamines by reaction of the anhydride group with the hydroxyl or amine groups.